Sonic generator



Nov. 2, 1965 R. s. SOLOFF 3,214,846

SONIC GENERATOR Filed Oct. 12, 1962 2 Sheets-Sheet 1 INVENTOR.

ROBERT S. SOLOFF Nov. 2, 1965 R. s. SOLOFF 3,214,846

SONIC GENERATOR Filed Oct. 12, 1962 2 Sheets-Sheet 2 RELATIVE ENERGYPERCENTAGE INVENTOR. ROBERT S. SOLOFF ATTORNEY United States Patent3,214,846 SONIC GENERATOR Robert S. Soloti, Brooklyn, N.Y., assignor, bymesne assignments, to Branson Instruments, Incorporated, Stamford,Conn., a corporation of Delaware Filed Oct. 12, 1962, Ser. No. 230,094 2Claims. (Cl. 34-142) This invention relates to a sonic dryer and to asonic generator producing intense sonic vibrations from a compressed gaswhistle without a concomitant blast of compressed gas.

It has been proposed to accelerate the drying of finely divided solidsby passing them through a dryer of conventional design, at one end ofwhich is a high powered whistle operated by compressed gas, usuallycompressed air. The resulting sonic vibrations in the dryer acceleratethe drying of the solid particles. However, a serious problem hasarisen. In order to produce intense sonic vibrations a very large volumeof compressed air is necessary and this produces a blast of air alongwith the sonic vibrations. The blast has seriously interfered withproper drying and has sometimes blown out solid particles which hasproduced a serious dust hazard. As a result the theoretically attractiveconcept of sonic drying has achieved but little practical utility.

The present invention has for its heart a compressed air or gas whistlewhich produces intense sonic vibrations without any accompanying blastof air. The large volumes of air escape substantially at right angleswithout interfering with the production of the sonic vibrations. Whenthis generator is mounted in a conventional dryer the intense sonicvibrations are imparted to the air in the dryer which moves slowly andthe blast of air pro ducing the sonic vibrations escapes at right anglesto the generator and does not enter the dryer. There is thus obtainedthe intense sonic vibrations without any air blast and the dryer can beoperated with a gentle stream of warmed air for optimum drying. The fulleffect of the sonic vibrations is retained without any of the drawbacksencountered previously as a result of the air blast.

Reference has been made to sonic vibrations. For best drying purposesnormally this is a high frequency sound, for example of the order of10,000 cycles. The invention is, however, in no sense limited to theparticular frequency of sonic vibrations used. They may be higher orlower, and even extend into the ultrasonic region. However, as will bepointed out, the frequency of the sound is connected in a criticalmanner with other dimensions of the generator and so, while varioussound frequencies may be used, once a sound frequency is chosen it willhave to be maintained unless the generator is readjusted or rebuilt todifferent dimensions.

The invention will be described in greater detail in connection with thedrawings in which:

FIG. 1 is a section through a dryer;

FIG. 2 is a detailed section on an enlarged scale of the sonicgenerator, and

FIG. 3 is a graph of variation of sonic intensity with generator elementdimensions.

The dryer, which is conventional in form, is shown with a rotatable drum1 provided with vanes for lifting and dropping particulate matterthrough the atmosphere in the dryer. The drum of the dryer is turned bygears 3 from a driving source (not shown). At one end is a feed hopper 4which feeds wet or damp particulate solids into one end of the dryer.This is surrounded with an air introducing annulus 6 through which warmair is introduced at relatively slow speeds. At the other end of thedryer there is an outlet chute through which introduced air escapes andalso the dried solids particles.

Patented Nov. 2, 1965 In this end of the drum there is the entrance pipe7 of the sonic generator which is shown in detail in FIG. 2. Theentrance pipe 7 is attached to the dryer by means of the flange 8 andbolts 9.

Turning now to FIG. 2 the entrance pipe 7 is connected to a block ofmetal 10 through pins 16. The block 10 has a hollowed tapered portion 11in which is located centrally a spindle 15 on which is mounted a cupshaped resonating cavity 14. The fastening is made permanently by thepin 18. A connection to a source of high pressure compressed air 12 isalso fastened to the block 10. The spindle 15 forms with the hollowedportion 11 a nozzle 13 through which the compressed air escapes atsupersonic speeds. This blast strikes the resonator 14. The blast of airproduces intense sonic vibrations and passes out along the sloping endof the reflecting surface 17, through the space between the tube 7 andthe block 10. The violent sonic vibrations traverse the tube 7 throughrelatively stagnant air with no sub stantial portion of the air blastwhich generates the sound flowing through the tube 7. The sonicvibrations, largely in the form of standing waves, continue through therelatively gently moving air in the dryer, accomplishing the effect ofincreased drying, which is the purpose of all sonic dryers.

The dimensions of the tube 7 are quite critical for optimum efiicieney.This tube may be considered acoustically as an open organ pipe, and thesonic vibrations set up a standing wave phenomenon within the tube.Ordinarily, the greatest intensity of energy is produced a half wavelength from the sonic generator, and so one would expect that formaximum efficiency the tube 7 should be a half wave length long for theparticular sonic frequency employed. It has been found that this isexactly what should not be done. For maximum efficiency the tube shouldbe two half wave lengths long. This is directly contrary to ordinaryacoustic experience, but it is observed with complete regularity and isa characteristic of the sonic generator of the present invention.

FIG. 3 shows three points corresponding to three tube lengths, in theform of a bar graph, one being a single half wave length, as shown onthe abscissa, the second being the preferred two half wave lengths, andthe third, three half wave lengths. In an ordinary organ pipe, acoustictheory specifies that maximum sound energy is produced at a length ofhalf a wave length, falling off for successive half wave lengths in anexponential manner. FIG. 3 shows that maximum intensity is obtained witha tube length of two wave lengths, the theoretically best length of asingle half wave length being 2 db down, or about 63%, and even thethird half Wave length is only down 1 db, and so is considerablystronger than the theoretically preferable single half wave length tube.The reasons for this anomalous behavior of the sonic generator of thepresent invention have not been rigorously established and so theinvention is in no sense intended to be limited to any particular theoryas to why ordinary acoustic practice does not hold in the presentinvention. Needless to say, the length of the tube 7 is adjusted to betwo half wave lengths long for the particular frequency to be used. Thisfrequency can be determined by air pressure and location of theresonator 14 and should be accurately fixed. The particular frequencychosen is of much less significance than the accurate dimensioning ofthe tube 7 for the frequency used.

While the sonic generator of the present invention finds its greatestpractical field of utility in sonic dryers it is of course not limitedto this use and may be employed anywhere where it is important togenerate intense sonic vibrations without an accompanying blast of gas.It should be noted that in the present invention the blast of air isejected at an angle to the tube 7. It is essential that there bebaflling means which prevent this blast from moving forward and mixingwith the sonic vibrations at the end of the tube 7. In the case of thedryer the end wall of the dryer forms its bafile.

The invention was illustrated in connection with a dryer whichrepresents a substantially incloscd space. Standing waves are thereforeset up and so no special directing means need be attached to the tube.When the invention is used with or in relatively unconfined spacesdirecting elements such as horns are advantageously attached to thetube. The horn shapes are well known and are therefore not illustratedin the drawings. Cones and exponential horns are among the most commonshapes. They all act as baflles, but when maximum coupling to unconfinedair is desired exponential horns exhibit somewhat greater efiiciency.Due to the high frequencies the difierence in coupling between cones andexponential horns is not very great as it is at lower frequencies.

The phenomenon is quite diflerent from that of a toroidal acousticreflector which has been proposed and which leads a blast of air aroundand backward by reason of the shape of its surface. With such areflector no tube analogous to the tube 7 is used. The present inventionis strictly limited to the combination of such a tube of definite lengthwith a sonic generator of the, resonating cavity type.

I claim:

1. A sonic generator comprising,

(a) a nozzle adapted to carry gas under pressure at supersonicvelocities,

(b) a sonic cavity resonator axially aligned with said nozzle, andspaced therefrom to produce sonic vibrations of a predeterminedwavelength,

(0) a reflecting element surrounding the nozzle and,

(d) an open ended resonant tube surrounding the cavity and connected tothe reflector to provide a peripheral escape slot for air blast, saidtube having a length approximately equal to two half wave lengths of thesonic vibrations. v

2. A sonic dryer comprising in combination (a) a drum,

(b) means for rotating the drum slowly, and means carried by the drumfor distributing finely particulate material through the atmosphere inthe drum,

(c) means for introducing particulate material to be dried in one end ofthe drum, means for maintaining a slow movement of atmosphere throughthe drum, and

(d) a sonic generator according to claim 1, the tuned tube thereofprotruding into one end of the drum, said drum end being sealed againstair blast from the sonic generator.

References Cited by the Examiner UNITED STATES PATENTS 1,245,517 11/17Scuterud 84410 2,344,7 5 4 3/44 Vang.

2,413,420 12/46 Stephanofl.

2,576,297 11/51 Horsl'ey et al. 34-4 3,064,619 11/62 Fortman 116l3WILLIAM F. O DEA, Primary Examiner. NORMAN YUDKOFF, Examiner.

1. A SONIC GENERATOR COMPRISING, (A) A NOZZLE ADAPTED TO CARRY GAS UNDERPRESSURE AT SUPERSONIC VELOCITIES, (B) A SONIC CAVITY RESONATOR AXIALLYALIGNED WITH SAID NOZZLE, AND SPACED THEREFROM TO PRODUCE SONICVIBRATIONS OF A PREDETERMINED WAVELENGTH, (C) A REFLECTING ELEMENTSURROUNDING THE NOZZLE AND,